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Yes, obviously feathers are not invested with blood vessels...  A spread
wing exposes more of its surface (including skin) than a folded wing -- I
allowed *solely for the sake of argument* that this MIGHT enhance (slightly)
transfer of environmental heat to (subcutaneous) blood vessels in the wing.

Perhaps my message wasn't clear... I am skeptical that wing-spreading in
these birds is about thermoregulation.  And even IF some degree of
thermoregulation occurs, it is best understood as an epiphenomenal
consequence of spreading wings to dry them.

(I believe that Erlich et al. state that Anhingas are thermoregulating but
cormorants are drying off).

David Wright
Miami Shores

on 10/16/02 3:18 PM, Brad_Bergstrom at [log in to unmask] wrote:
> David Wright wrote:
>
>> Bird wings do have arteries and veins.  As Brad alluded, these vessels
>> are not generally set up for serious heat transfer (e.g., rete mirabile)
>> in birds (anhingas in particular?).  A spread wing should absorb heat
>> better across its total surface better than a folded wing
>
> Well, the [very small] part of the wing that is covered in skin has blood
> vessels, permanently.  However, the vast majority of the surface area of
> the wing is formed by the remiges or flight feathers.  These feathers have
> blood vessels only when they are growing.  A set of mature feathers,
> however, is completely inert.  Dead.  The dermal pith inside the feather
> shaft is resorbed when growth is completed, and the inferior umbilicus
> (the pore that allows connection of the growing feather with the skin and
> circulatory system) is sealed off with a plug of keratin.  Nothing inside
> the feather shaft except air after that.  After molt is completed, the
> feathers are not set up for ANY heat transfer.  So, unless an Anhinga
> always has some growing wing feathers (certainly not the case), the wing,
> itself, is not acting as a radiator or heat collecter (unless you're
> talking about some bare areas near the armpit).
>
> Kenn Kaufmann (1996, Lives of North American Birds) says that both
> cormorants and anhingas dry their waterlogged wings after diving.  I seem
> to have misplaced my copy of Ehrlich, et al. (Birder's Companion), but I'm
> sure somebody out there has it handy.  I'll bet they say the same thing.
>
> Brad
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